The primary interest of Joseph Mallord William Turner (1775-1851) as a painter was the behavior and appearance of light in the atmosphere. He was aware—from reading scientific publications and corresponding with their authors—that different hues could be obtained by splitting white light into its component wavelengths. Conversely, primary colors could be combined to produce white light. With this principle in mind, Turner set himself the task of representing the extraordinary effects of atmospheric light on canvas and paper. It wasn't as simple as mixing colors to paint what he saw. When two pigments are mixed together, the resulting compound is often less brilliant than the separate pigments before mixing, because some of the light reflected by one of the mixed pigments is typically absorbed by the other. To preserve the intensity of component hues, Turner painted little patches of different colors close together, so that the combinations of colors would be perceived in the eye, unadulterated by the mixing of pigments on the palette. This visual effect, known as optical mixing, not only allows the perception of blended color without loss of intensity, but also creates a flickering or glimmering sensation as the eye and the brain work together to mix the perceptions of color.
Cole TB. The Burning of the Houses of Lords and Commons, 16 October, 1834. JAMA. 2010;304(18):1990. doi:10.1001/jama.2010.1626